We propose to study the concentration and patterns of secretion of gonadal hormones during the annual reproductive cycles of lizards, crocodilians, and turtles by steroid radioimmunoassay, and relate these changes to naturally occurring species-typical reproductive behavior patterns. Experiments will also be conducted to determine the hormonal control of male and female reproductive behavior. Direct versus indirect action of androgens on central and peripheral tissues in reptiles will be examined by behavioral testing and histological examination of the renal sex segment and oviduct in response to exogenous steroids and their antagonists. Steroid-sensitive sites in the male and female brain of lizards have been identified by autoradiography and lesion and intracranial steroid implantation experiments are proposed to investigate the role of these areas in regulation of social behavior.